Employer of a superior, fault free service (4)

I believe the answer is:

user

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'employer' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for user that I've seen before include "Utiliser" , "Drug taker" , "Patron" , "Maybe one needing pot" , "Tech support caller?" .)

I've seen this clue in the Evening Standard.

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